The Omega-3 Index, a biomarker developed by Drs. Bill Harris and Clemens von Schacky, measures the amount of EPA + DHA as a percentage of total fatty acids in red blood cell membranes. The Omega-3 Index has been proposed as a measurable biomarker of sudden cardiac death risk. and may provide a means of standardizing methodologies that produce equivalent measures in clinical trials, allowing researchers to interpret clinical trial outcomes more accurately.
Since its inception in 2004, the Omega-3 Index has been assessed in numerous populations and correlates closely with health. Some of the most compelling findings include:
Measuring omega-3 concentrations in red blood cells provides reliable assessments of long-term intake, is more accurate than measuring omega-3 concentrations in plasma or serum (which fluctuate daily), and is highly reflective of fatty acid composition in most tissues, except the brain.    Determination of an Omega-3 Index relies on the use of specific, standardized laboratory procedures that provide consistent, valid results.
Most people living in the United States and other western countries have an Omega-3 Index of approximately 4 percent. Robust evidence suggests, however, that an Omega-3 Index of 8 to 11 percent provides the greatest health benefits. To raise an individual's Omega-3 Index from 4 percent to the recommended range of 8 percent or greater, intake should be between 1,750 and 2,500 milligrams (1.75 and 2.5 grams) per day._
It is noteworthy that gender and age influence Omega-3 Index scores in humans. A meta-analysis of 51 studies found lower levels of arachidonic acid (an omega-6 fatty acid) and DHA as a percentage of plasma lipid in men compared to women, suggesting that gender-specific differences occur in long-chain fatty acid metabolism, possibly modulated by sex hormones. Similarly, young women tend to have higher DHA and lower EPA levels than older women, suggesting that younger women have an enhanced ability to convert EPA to DHA, likely due to DHA's important role in reproduction and development. Furthermore, fatty acid levels tend to shift with age such that the Omega-3 Index is higher and linoleic acid levels are lower in older age.